If you need 1/2" drive levels of torque on a 10mm bolt head, I think the battle is already lost.

A couple weeks ago I was doing some R&R on my car. Right rear wheel bearing (which turned into a lot more besides, as rust never sleeps).
I put 1/4" drive levels of torque (short breaker bar) on a 6mm bolt that retained one of the wheel speed sensors; this after soaking the area for several nights with PB Blaster.
Yeah, the sumb!tch snapped right off...flush with the torque arm.

It took a couple hours to properly drill the old bolt out and tap the hole but I dunnit.